The present invention relates generally to ablation devices and, more specifically, to optical feedback radiofrequency (RF) ablators and ablator tips.
Proposed optical-feedback catheters such as those of Biosense-Webster mainly employ an RF catheter in which the thermally ablative RF tip is also capable of the optical detection of the thermal lesions the RF tip forms. See, e.g., US2008/0119694, which is incorporated herein by reference in its entirety. The thermally ablative RF tip has a hollow RF electrode and the outer RF electrode surface is electrically conducting and therefore can deliver RF ablation by electrical contact to target tissue. Inside the hollow metal-coated or metal-walled RF tip electrode are two radially isolated optical elements or chambers, each of which is connected to a separate optical fiber running along the catheter lumen to the proximal catheter handle. The first fiber delivers optically broadband illumination light to the first tip optical cavity (the emission cavity) from which the light emits into nearby tissue through a number of optical vias bridging the tissue and the emission optical element. Thus the emission optical element acts to omni-directionally spray or distribute emanating broadband excitation light from the numerous optical emission vias into the contacting tissue. Note that the omni-directional 360 degree optical output assures that tissue which contacts only one side face of the tip (which is typical) will be illuminated without requiring axial tip rotation. A second optically isolated element in the RF tip is the optical reception element. It is optically coupled to the tissue by a second separate set of interspersed optical vias which receive backscattered light from tissues (i.e., received light which comprises incoming backscattered illumination light). The optical reception element is coupled to the second optical fiber which is used to route incoming backscattered light from the tip back to the catheter handle and to an optical sensor such as an optical spectrometer. The received or backscattered light spectrum is wavelength-scanned by the spectrometer looking for amplitude changes at various wavelengths particularly those corresponding to changing optical absorption or scattering mechanisms in the tissue. Thus, for example, thermal ablation lesions reduce water content in tissue so that optical reflectance or backscattering is affected at one or more wavelengths sensitive to water content. Optical spectroscopy has been used for real time assessment of RF cardiac tissue ablation. See Stavros G. Demos & Shiva Shararch, “Real Time Assessment of RF Cardiac Tissue Ablation with Optical Spectroscopy,” Optics Express, Vol. 16, No. 19 (Sep. 15, 2008), which is incorporated herein by reference in its entirety. Note that RF ablations are usually done on target tissue either contacting the side of the RF tip or contacting the end (forward looking end) of the RF tip. Thus most preferably, by omni-directional performance, is meant optical lesion detection of RF lesions both radially (sideways at any rotational angle between 0 and 360 degrees) and forwardly such as with the tip sitting roughly perpendicular to the tissue target or at a tilted angle thereto such as between 0 and 60 degrees.
It has been considered advantageous if not required to optically isolate the two optical elements and their respective sets of optical vias. The argument for this is so as not to saturate the optical receiver (the wavelength spectrometer) with ingoing light which would otherwise travel within the tip directly from the emission fiber to the collection fiber without ever having been emitted from the tip and tissue-scattered. In order to optically isolate the two elements and their respective via sets yet still have omni-directional emanation and reception, the tip is configured to have the emission element within the reception element and it is isolated from it by a radial opaque wall or film. Thus the emission vias, although they pass through the outer reception element, do not dump light directly into the reception element. The reception element vias pass light into the outer annular reception element so that they never penetrate the interior emission element. This arrangement totally isolates the outgoing and incoming optical paths so that reception signal/noise ratio is maximal per such an argument.
A significant drawback of that double walled optical element tip design and interspersed yet isolated optical via sets is that it is very hard to make in terms of difficulty and manufacturing yield and typically requires a double shell structure wherein penetrating optical vias must all be each individually optically isolated. Another problem is that the cumulative area of the emanation optical vias and the cumulative area of the reception optical vias are each quite small; otherwise, the metal shell has too many holes in it to be mechanically sound. The prior art proposed designs such as this also make it difficult to provide a saline irrigated (cooled) RF electrode unless irrigation flow paths double as optical paths. This is considered a limit on the number and scope of possible product designs and not necessarily a technical issue.